1. Field of the Invention
This invention relates to a matrix display apparatus that has a dielectric substance between its substrates. More particularly, it relates to a matrix display apparatus that is used for a liquid crystal display apparatus, an electric luminescence (EL) display apparatus, a plasma display apparatus, etc.
2. Description of the Prior Art
In matrix display apparatuses, such as in a liquid crystal display apparatus, EL display apparatus, or plasma display apparatus, voltage is applied between the electrodes for the display, and the optical characteristics of the display medium that is positioned between the electrodes for the display are modulated, so that a display pattern is formed. The method for the driving of the electrodes for the display can be the simple matrix method, the active matrix driving method, or other well-known methods.
One example of a display apparatus that makes use of the simple matrix method is shown in cross-section in FIG. 6. On glass substrate 31, scanning wires 33 with a thickness of 2000 .ANG. made of Mo, scanning transparent electrodes 32 with a thickness of 1000 .ANG., an insulating film 34 with a thickness of 2000 .ANG. made of SiO.sub.2, and an orientation film 35 are formed in that order. The scanning transparent electrodes 32 act as the display electrodes, and the scanning wires 33 act as driving wires that drive the scanning transparent electrodes 32.
On glass substrate 37, which faces the substrate 31 with a liquid crystal layer 36 therebetween, there are signal wires 39 with a thickness of 2000 .ANG. made of Mo, transparent signal electrodes 38 with a thickness of 1000 .ANG., and an orientation film 40. The transparent signal electrodes 38 act as the electrodes for the display, and the signal wires 39 act as the driving wires for the driving of the transparent signal electrodes 38 for signaling. FIG. 7 is a planar view of this display apparatus seen from the side of substrate 37. As shown in FIG. 7, one part of each of the scanning transparent electrodes 32 and the entire surface of the corresponding scanning wire 33 are layered together, so that they are electrically connected. In the same way, one part of each of the transparent signal electrodes 38 and the entire surface of the corresponding signal wire 39 are layered together, so that they are electrically connected. The portion of the scanning transparent electrode 32 that is not layered together with the scanning wire 33 and the portion of the transparent signal electrode 38 that is not layered together with the signal wire 39 overlap each other, so that the region of overlap constitutes a picture element of the display.
FIG. 8A is one example of an active matrix substrate that can be used in an active matrix display apparatus. FIG. 8B is a cross-sectional diagram of the display apparatus that uses the active matrix substrate of FIG. 8A, cut along the line b--b in FIG. 8A. On glass substrate 1, there is formed a base coat film 3 over its entire surface, and on the base coat film 3, gate bus wires 4 that act as scanning wires are disposed so as to form a latticework with source bus wires 5 that act as signal wires. In the space between the gate bus wires 4 and the source bus wires 5, there is sandwiched a base insulating film 11 (see below). A portion of each of the gate bus wires 4 acts as a gate electrode 9. There are picture element electrodes 6 made of a transparent conductive film (made of indium tin oxide) in the respective rectangles surrounded by the gate bus wires 4 and source bus wires 5, the picture element electrodes 6 forming a matrix. The picture element electrodes 6 act as the display electrodes. Near the edge of the picture element electrode 6, there is a switching element formed from a thin-film transistor (TFT) 7. A drain electrode 13 of TFT 7 and the picture element electrode 6 are connected electrically by drain wire 25, which acts as a drive wire for the picture element electrode. The TFT 7 is placed on the gate bus wire 4. Source electrode 15 and source bus wire 5 of the TFT 7 are connected to each other by branch wire 8.
The sectional structure near TFT 7 will be described with reference to FIG. 8B. On the top of the gate electrode 9 that forms one part of the gate bus wire 4, there is a gate insulating film 10 obtained by the anodic oxidation of the surface of said gate electrode 9. On the top of this film, there are layered base insulating film 11, which also acts as a gate insulating film, an intrinsic semiconductor layer 12 made of amorphous silicon (a-Si), a semiconductor-layer protective film 16 that protects the upper surface of the intrinsic semiconductor layer 12, and n-type semiconductor layers 14. On the n-type semiconductor layers 14, there is formed a source electrode 15, which is connected with branch wire 8, and a drain electrode 13, which is connected with picture element electrode 6. The n-type semiconductor layers 14 provide ohmic contact between the source electrode 15 and the drain electrode 13. The protective film 17 covers almost all of the upper surfaces of TFT 7 and the picture element electrode 6, and on the upper surface of the protective film 17, there is an orientation film 19.
On the inner surface of glass substrate 20 that faces glass substrate 1, a color filter layer 21, an opposing electrode 22, and an orientation film 23 are disposed, in that order. Between the glass substrates 1 and 20 there is a liquid crystal layer 18, which acts as a display medium. To improve the reproducibility of colors when a color display is made, a light-proof film (not shown) can be provided on the active matrix substrate or on the opposing substrate, so that the light-proof film is layered on part of the outer portion of the picture element electrodes 6.
In the matrix display apparatus shown in FIG. 6, there can occur a defective connection in the driving wires 33 (39) connected to the display electrodes 32 (38). Also, with the active-matrix display apparatus shown in FIG. 8, there can develop a defective connection in the driving wires that are formed from the scanning wires 4 connected to TFT 7, the signal wires 5, and the picture element electrode driving wires 25 in the space between the picture element electrode 6 and the TFT 7. In addition, there may be a failure of contact between the picture element electrode driving wires 25 and the picture element electrodes 6. If such a failure takes place, a defect in the wiring or in a picture element occurs. Such defect causes decreased productivity, which is a problem in manufacturing.
In recent years, a means to overcome defects in matrix display apparatuses has been disclosed. A means by which laser light is used to treat defects such as a connection defect or a failure of contact, melting the metal of the electrode in this area, and thereby repairing the defect, has been disclosed in Japanese Laid-Open Patent Publication No. 61-56382. However, it is impossible at times to use this means to repair the defect if the metal to be melted is too thick, or in certain kinds of failure of connection.
Defects in wiring or in picture elements can be readily identified by the operation of the display apparatus, in a simple and accurate process. The defects can be identified by eye with the use of a lens, etc. However, to identify the location of a defect in the substrate before the display apparatus has been completed involves an inspection process that is complicated and requires a highly accurate means of measurement. The technique mentioned above in which laser light is used to repair defects is generally done before the completion of the display apparatus. When this method of irradiation with laser light is used after the display apparatus is completed to repair the picture element electrodes with a switching element, the insulation between the picture element electrode and the display medium may be damaged by the heat that is generated. With damaged insulating properties, it is impossible for the potential of the picture element electrode to be maintained even with the use of the switching element. The outcome is that the defect in the picture element is not actually repaired, and the defect is therefore still present even after repair. For these reasons, defects must be repaired by this technique before the completion of the display apparatus.